This application claims priority under 35 USC §119 to Korean Patent Application No. 2007-29324 filed on Mar. 26, 2007 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates generally to communication systems, and more particularly, to a signal generation apparatus for generating in-phase and quadrature (I/Q) signals with compensation of offset voltage and phase delay in a phase compensator.
2. Background of the Invention
In general, a zero-IF structure and an image rejection structure in a receiver or transmitter of a communication system typically uses an in-phase signal (hereinafter, referred to as an “I signal”) and a quadrature-phase signal (hereinafter, referred to as a “Q signal”) that are desired to have a phase difference of about 90°. FIG. 1 shows a block diagram of a frequency converting apparatus 10 which may be used in a receiver or transmitter according to the prior art. Referring to FIG. 1, the frequency converting apparatus 10 includes a signal generation circuit 12, a first mixer 18, and a second mixer 20.
The signal generation circuit 12 generates the I signals Ip and In as differential signals and generates the Q signals Qp and Qn as differential signals. The signal generation circuit 12 includes a voltage control oscillator (VCO) 14 and an I/Q signal generator 16. The voltage control oscillator 14 generates differential oscillating signals In+ and In−. The I/Q signal generator 16 generates the differential I signals Ip and In and the differential Q signals Qp and Qn from the differential oscillating signals In+ and In−. The pair of signals Ip and Qp are desired to have a phase difference of 90°, and the pair of signals In and Qn are desired to have a phase difference of 90°.
The first mixer 18 mixes a wireless (i.e., radio frequency) input signal RFIN and at least one of the I signals Ip and In to generate an in-phase intermediate frequency signal IIF. The second mixer 20 mixes the wireless input signal RFIN and at least one of the Q signals Qp and Qn to generate a quadrature-phase intermediate frequency signal IQF. When the phase difference between the signals Ip and the Qp or the signals In and the Qn is not accurately maintained at 90°, an image rejection characteristic of each of the first and second mixers 18 and 20 may disadvantageously be deteriorated.
A plurality of phase compensators (not shown in FIG. 1) compensate for a phase difference between the In and Qn signals to be maintained at 90°. However, the phase difference between the Ip and Qp signals may not be accurately maintained at 90° because of an offset voltage and a phase delay in the phase compensator. For example, the phase delay may be due to differences through multiple transfer paths within the phase compensator.
In addition, the Ip and Qp signals or the In and Qn signals may not have an accurate phase difference of 90° from variable parameters such as the manufacturing process, a supply voltage, and temperature. Thus, a signal-to-noise ratio (SNR) is deteriorated, and consequently a receiving sensitivity of a receiver or a transmitting sensitivity of a transmitter in a communication system is deteriorated.